In the gearing mechanisms known from conventional practice, shifting elements are preferably hydraulically activated due to the demand for high power density. A central hydraulic control device normally produces a control pressure in a hydraulic system by way of pressure controllers and valve units placed downstream from them, along with the hydraulic fluid flows necessary to actuate the shifting elements. In the operation of an automatic gearing mechanism, the central hydraulic control device is supplied by a permanently driven oil pump, or as the case may be, a pumping device by way of which the hydraulic system of a gearing mechanism is acted upon by the hydraulic-fluid volume flows that are required in all operating states of the gearing mechanism.
However, this has the disadvantage that the hydraulic-fluid volume flow delivered by the pumping device does not depend on requirements, but rather on rotation speed, i.e., is dependent on the number of revolutions produced by the main engine of the vehicle, the characteristic curve of the pumping device being designed for an operating state in which the pumping device displays its minimum delivery volume, and in which the users of the gearing mechanism, which have to be supplied with control pressure and hydraulic fluid via the hydraulic system, demonstrate a high requirement for hydraulic fluid. In this way, the pumping device, at high drive speeds, i.e., in high rotational-speed ranges of the driving engine, circulates hydraulic-fluid volume flows in the hydraulic system that are not needed to this extent by the hydraulic users of the gearing mechanism. In these operating ranges, the pumping device has an unnecessarily high power consumption, which reduces the efficiency of an automatic gearing mechanism and leads to an increase in fuel consumption in vehicles equipped with this type of automatic gearing mechanism compared to vehicles equipped with manual transmissions, whose shifting elements are essentially mechanically actuated.
In addition, hydraulic systems with gearing mechanisms that are configured as hydraulically actuatable shifting elements are known, in which a central feed line is supplied by a central pumping device with hydraulic fluid that is compressed to a predefined level of pressure, similar to a common-rail fuel-injection system of a diesel combustion engine. The feed line can be brought into functional connection with the shifting element via pressure controllers arranged in the proximity of shifting elements to be hydraulically actuated in such a way that the shifting elements are supplied or, as the case may be, acted upon by the pressure and hydraulic-fluid volume flows necessary to actuate them.
A disadvantage of this method is that the portion of the hydraulic fluid of an automatic transmission that is normally supposed to be raised to a lower level of control pressure, such as a lubricant-circuit or cooling-oil circuit level, is condensed to the high holding-pressure level of the portion of the hydraulic fluid of an automatic transmission that is intended for the actuation of multiple-disk clutch or multiple-disk brakes. This also means that the power consumption of the pumping device in these hydraulic systems is higher than that needed to supply the users of an automatic transmission. This leads to impairment of the efficiency of an automatic transmission and to an undesirably high fuel consumption by the vehicle.
The present invention is, therefore, based on the task of providing a device for controlling and/or regulating at least one hydraulically activatable shifting element of a gearing mechanism device, by way of which a gearing mechanism can be operated at a high degree of efficiency, and to create a gearing mechanism that can be operated at a high degree of efficiency.